Re: New Study Claims Mars Dry for 4 Billion Years

>>>>> "m" == msadkins04 <msadkins04@xxxxxxxxx> writes:

m> Today on the Web there was an item at space.com by Senior Science
m> Writer Robert Roy Britt, announcing the results of a study due to
m> appear in the July 22 issue of the journal Science, in which
m> Caltech graduate student David Shuster and Asst. Prof. Benjamin
m> Weiss suggest that Mars hasn't had "large areas of freestanding
m> water for four billion years", but don't rule out "pockets of
m> isolated water in geothermal springs for periods of time".

Some of your comments may be outdated, now that the actual article has
appeared, but just in case that isn't so....

m> The study is based upon argon decay analysis of the remaining argon
m> content of seven meteorites "known to have arrived from Mars after
m> millions of years in space". The study relies on a formula for
m> argon decay that varies with temperature. [...]

Not decay, diffusion. (Of course, this confusion may have been
generated by the space.com article.) Decay implies a nuclear
reaction, which shouldn't be affected by temperature (at least not at
the temperatures of interest here).

Diffusion, OTOH, can be affected by temperature. The hotter a rock
is, the easier it is for gasses to diffuse through it.


m> Offhand, there seem to be a number of assumptions to be justified.
m> Whether the study does so successfully remains to be seen, though
m> the fact that these represent elementary issues suggests that they
m> wouldn't be overlooked.

Always be careful about assessing the validity of a scientific paper
based on its press coverage.

m> First, how is it known that the rocks weren't in space for merely
m> "millions of years" but perhaps for billions of years? [...]

Cosmic ray exposure. There is a host of material about this on the
Web, but, simply put, the longer a rock is in space, the more cosmic
rays to which it is exposed, and the more isotopes are produced in the
rock from nuclear reactions.

m> Second, what were the climate patterns on Mars up until the time
m> these rocks became spaceborn? Could they have originated in a part
m> of Mars that was "very cold" without implicating the same climate
m> for all the rest of the planet?

I suppose that is the case. Of course, as one would sample more and
more meteorites, this case would become less and less likely.

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